1. Field of the Invention
The present invention relates generally to a light irradiating device, optical pickup device with the same, and method of adjusting the light irradiating device, which is suitably used in various recording apparatuses having a function of recording information in optical information recording media, such as digital versatile discs, etc.
2. Description of the Prior Art
Recently, there has been realized a digital versatile disc (DVD) that allows an image quality higher than that of a laser disc and a running time longer than 130 minutes on a single side. Such a DVD has a capacity of about 4.7 GB on a single side, which is seven times greater than that of a compact disc-read only memory (CD-ROM).
For recording/reproducing of an optical information recording medium such as the optical disc, an optical pickup device is used having the construction in which optical devices such as a semiconductor laser (LD: light emitting device), a polarization beam splitter, a collimating lens, a xc2xcxcex plate, an object lens and a PIN-photo diode (PIN-PD: light receiving device) are arranged along an optical axis.
The optical pickup device narrows light emitted from the semiconductor laser to a predetermined diameter by the collimating lens and the object lens, and then condenses the narrowed light onto an optical information recording medium. In this case, in order to maximally increase energy of a light spot condensed onto the optical recording medium, the light emitted from the semiconductor laser must be used as efficiently as possible, and a numerical aperture (NA) of the collimating lens must be set to as large as possible.
However, on a plane perpendicular to an optical axis of light emitted from the semiconductor laser, a light intensity distribution is represented by a Gaussian distribution in which light intensity is high at its center, and becomes rapidly lower from the center to the sides. Therefore, parallel light obtained by converting the emitted light using the collimating lens, or diffused light with a predetermined radiation angle, also has the same light intensity distribution as the Gaussian distribution. In this case, since the size of the spot of light condensed onto the optical information recording medium by the object lens is increased, various problems such as a decreased recording density of the optical information recording medium, a deterioration of reproduced signals, etc., may occur.
Therefore, in order to solve the above problems, an optical pickup device using a beam shaping prism is proposed and provided practically.
FIG. 12 is a view showing the construction of a conventional optical pickup device using a beam shaping prism. Referring to FIG. 12, reference numeral 1 designates a semiconductor laser (LD: light emitting device), reference numeral 2 a collimating lens, reference numeral 3 a beam shaping prism in which a pair of prisms 3a and 3b are arranged facing each other, reference numeral 4 an object lens, and reference numeral 5 an optical disc (optical information recording medium).
The semiconductor laser 1 emits light, for example, blue light having a wavelength of 430 nm, or red light having a wavelength of 635 nm. A radial diffusion angle of the emitted light has radiation properties different in the horizontal and vertical directions with respect to a plane of polarization. For example, a diffusion angle in a vertical direction is about 30 to 40 degrees, and a diffusion angle in a horizontal direction is about 10 degrees.
In the optical pickup device, light radially emitted from the semiconductor laser 1 is converted into parallel light by the collimating lens 2. Intensity distribution of light sequentially transmitted through and diffracted by the respective prisms 3a and 3b constituting the beam shaping prism 3 is converted from the Gaussian distribution to a flat distribution. Then, the transmitted and diffracted light is narrowed to a predetermined diameter by the object lens 4, such that it is condensed onto a recording surface of the optical disc 5.
Light reflected from the recording surface of the optical disc 5 is converted into parallel light by the object lens 4, sequentially transmitted through the beam shaping prism 3 and the collimating lens 2, and then received by the PIN-PD (light receiving device) via an optical system such as a polarizing beam splitter (not shown). The received light can be obtained as reproduced signals.
FIG. 13 is a graph showing light intensity distributions before and after light is transmitted through the beam shaping prism 3. In the graph, a curve A is a light intensity distribution before light is transmitted through the beam shaping prism 3, and a curve B is a light intensity distribution after light is transmitted through the beam shaping prism 3.
Referring to FIG. 13, the light intensity distribution A before light is transmitted through the beam shaping prism 3 is a Gaussian distribution. However, as light is transmitted through and refracted by the beam shaping prism 3, the light intensity distribution is converted into the light intensity distribution B, in which the light intensity is lower in its center than that of the Gaussian distribution, and becomes gradually lower from the center to the sides, that is, flatter than the Gaussian distribution.
As described above, the light emitted from the semiconductor laser 1 has the light intensity distribution B flatter than the Gaussian distribution over the entire range of a valid diameter Dc of the collimating lens 2 by the transmission of light through the beam shaping prism 3. Therefore, if the recording density of an optical information recording medium is decreased, there is a little concern about deterioration of reproduced signals, or other problems.
Meanwhile, in the conventional optical pickup device using a beam shaping prism, the beam shaping prism 3 is constructed such that the pair of prisms 3a and 3b are arranged facing each other. Therefore, an optical axis is apt to be refracted and be eccentric, so it is difficult to adjust the assembly of the optical pickup device using a beam shaping prism. Further, the conventional optical pickup device is problematic in that it employs the pair of prisms 3a and 3b, so it is difficult to miniaturize the optical pickup device. Further, the conventional optical pickup device is problematic in that the number of optical parts is increased, thus causing the manufacturing process of the optical pickup device to be lengthened, and increasing manufacturing costs thereof.
Moreover, the conventional optical pickup device using a beam shaping prism is problematic in that astigmatism occurs if light transmitted through and refracted by the beam shaping prism 3 is not parallel light.
Further, a light emission wavelength of emitted light can be adjusted within xc2x15 nm of a desired wavelength by the semiconductor laser 1, while deviation of a radiation angle of the emitted light cannot be adjusted.
Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide a light irradiating device, optical pickup device with the same, and method of adjusting the light irradiating device, which can obtain light use efficiency required for recording/reproducing of an optical information recording medium, achieve a uniform light intensity distribution in a plane perpendicular to an optical axis, prevent refraction and eccentricity of the optical axis, simplify assembly and adjustment of the light irradiating device, minimize generation of astigmatism, and adjust deviation of a radiation angle of light emitted from a semiconductor laser.
In order to accomplish the above object, the present invention provides a light irradiating device, optical pickup device with the same, and method of adjusting the light irradiating device.
In accordance with a first aspect of the present invention, the present invention can be accomplished by the provision of a light irradiating device, comprising a light emitting device; a lens system for narrowing light emitted from the light emitting device to a predetermined diameter; and a secondary lens disposed between the light emitting device and the lens system; wherein each of the light emitting device and the secondary lens is fixed to an arbitrary position on an optical axis while allowing the light emitting device and the secondary lens to move independently along the optical axis.
In the light irradiating device, a secondary lens is disposed between the light emitting device and the lens system, thus allowing the composite focal distance of the lens system and the secondary lens to be a practical focal distance of the lens system.
The light emitting device and the secondary lens can each be independently moved along the optical axis to be fixed to an arbitrary portion on the optical axis, such that a lens system having a variable focal distance can be realized by moving the secondary lens along the optical axis on the optical axis between the light emitting device and the lens system.
In this case, if the radiation angle of light emitted from the light emitting device is less than a standard value, the numerical aperture (NA) of the lens system is reduced by increasing the focal distance of the lens system. Herewith, the center part of the light intensity distribution of the emitted light is used, thus realizing the uniformity of the light intensity distribution.
Further, if the radiation angle of light emitted from the light emitting device is higher than the standard value, the uniformity of the light intensity distribution of the emitted light can be maintained; however, use efficiency of the light intensity distribution of the emitted light is decreased. In this case, the numerical aperture (NA) of the lens system can be increased and use efficiency of the light intensity can be maintained at the standard value by reducing the focal distance of the lens system.
As described above, the light irradiating device can obtain light use efficiency and a uniform light intensity distribution required for recording/reproducing of an optical information recording medium.
Further, the light irradiating device can prevent refraction and eccentricity of the optical axis, and simplify its assembly and adjustment. Further, the light irradiating device can minimize generation of astigmatism, and adjust the deviation of a radiation angle of light emitted from the light emitting device.
In accordance with a second aspect of the present invention, a light irradiating device is provided having the above construction, wherein the lens system includes a collimating lens for converting the light emitted from the light emitting device into parallel light, and an object lens for narrowing the parallel light from the collimating lens to a predetermined diameter; and the collimating lens is fixed to an arbitrary position on the optical axis while allowing the collimating lens to move along the optical axis.
In the light irradiating device, the lens system has a collimating lens for converting the light emitted from the light emitting device into parallel light, and an object lens for narrowing the parallel light from the collimating lens to a predetermined diameter, wherein the collimating lens can be fixed to an arbitrary position on the optical axis by moving the collimating lens along the optical axis, thus obtaining light use efficiency and a uniform light intensity distribution required for recording/reproducing of an optical information recording medium, in an infinite optical system.
In accordance with a third aspect of the present invention, a light irradiating device is provided having the above construction of the first or second aspects of the present invention, and further comprising a housing for accommodating the light emitting device and the lens system therein, the housing having one or more holes formed in its side surfaces for detecting a position of the light emitting device or the lens system, or positions of both the light emitting device and lens system.
In the light irradiating device, one or more holes to detect the position of the light emitting device or the lens system, or positions of both the light emitting device and lense system, are formed in side surfaces of a housing which accommodates the light emitting device and the lens system, thereby enabling the positioning of the light emitting device or the lens system, or both the light emitting device and lens system, to be easily carried out in a short period of time.
In accordance with a fourth aspect of the present invention, a light irradiating device is provided having the above construction of the first, second or third aspects of the present invention, wherein at least one of the light emitting device and the lens system has a discerning mark formed thereon.
In the light irradiating device, a discerning mark is formed on the light emitting device or the lens system, or both of them, thus enabling the light emitting device or the lens system, or both of them, to be easily discerned, and improving working efficiency in their positioning operations.
In accordance with a fifth aspect of the present invention, an optical pickup device is provided comprising a light irradiating device in accordance with any of the first to fourth aspects of the present invention.
The optical pickup device can emit light having a light use efficiency and a uniform light intensity distribution required for recording/reproducing of an optical information recording medium to the optical information recording medium.
Further, the optical pickup device can prevent refraction and eccentricity of the optical axis, and simplify its assembly and adjustment. Further, the light irradiating device can minimize generation of astigmatism, and adjust the deviation of a radiation angle of light emitted from the light emitting device.
In accordance with a sixth aspect of the present invention, a method of adjusting a light irradiating device is provided, the light irradiating device having a light emitting device, a lens system for narrowing light emitted from the light emitting device to a predetermined diameter, and a secondary lens disposed between the lens system and the light emitting device, comprising the steps of varying a composite focal distance of the lens system and the secondary lens by moving the secondary lens along an optical axis; and moving the light emitting device along the optical axis, and allowing a light emitting point of the light emitting device to correspond to a composite focus of the lens system and the secondary lens.
The method of adjusting a light irradiating device can enable emission of light having a light use efficiency and a uniform light intensity distribution required for recording/reproducing of an optical information recording medium by varying a composite focal distance of the lens system and the secondary lens by moving the secondary lens along an optical axis and moving the light emitting device along the optical axis, and allowing a light emitting point of the light emitting device to correspond to a composite focus of the lens system and the secondary lens. Further, the secondary lens and the light emitting device can be moved along the optical axis, thus enabling the light irradiating device to be easily assembled and adjusted, and removing difficulty of assembly and adjustment of a conventional light irradiating device.
In accordance with a seventh aspect of the present invention, a method of adjusting a light irradiating device is provided, the light irradiating device having a light emitting device, a collimating lens for converting light emitted from the light emitting device into parallel light, an object lens for narrowing the parallel light from the collimating lens to a predetermined diameter and a secondary lens disposed between the collimating lens and the light emitting device, comprising the step of varying a composite focal distance of the collimating lens and the secondary lens by moving the collimating lens and the secondary lens independently along an optical axis, thus allowing the position of a composite focus of the collimating lens and the secondary lens to correspond to a light emitting point of the light emitting device.
The method of adjusting a light irradiating device can enable emission of light having a light use efficiency and a uniform light intensity distribution required for recording/reproducing of an optical information recording medium by varying a composite focal distance of the collimating lens and the secondary lens by moving the collimating lens and the secondary lens independently along an optical axis, thus allowing the position of a composite focus of the collimating lens and the secondary lens to correspond to a light emitting point of the light emitting device. Further, the collimating lens and the secondary lens can be moved along the optical axis, thus enabling the light irradiating device to be easily assembled and adjusted, and removing difficulty of assembly and adjustment of a conventional light irradiating device.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.